1. Field of the Invention
This invention relates to a magnetic disc cartridge comprising a jacket, a magnetic flexible disc or sheet rotatably accommodated in said jacket and used for recording and/or reproducing video signals obtained from an electronic still picture camera and, more particularly, relates to a magnetic disc cartridge whose jacket, is provided with display means for indicating the number of recorded circular tracks on the magnetic sheet and also provided with locking means for preventing said display means from an inadvertent modification of its precise indicating position.
2. Description of the Prior Art
An electronic still picture camera includes an image sensor unit which converts an incident light image of an object into electromagnetic image signals, and a recording unit for magnetically recording said image signals on a disc shaped flexible magnetic sheet. In a camera of this type, the magnetic disc or sheet is rotated at a constant angular speed around its rotation axis and a magnetic head supplied with image signals for one picture or field, is held in frictional and magnetic contact with the magnetic sheet, whereby the image information signals for one field are magnetically recorded on one circular track or two circular tracks. After the completion of an image recording the magnetic head is fed or moved in a radial direction of the magnetic disc to the next unrecorded track. In this way, the image signals corresponding to a plurality of pictures are successively magnetically recorded along concentric tracks of the magnetic sheet.
The applicant has already proposed a magnetic disc cartridge, in which a disc-shaped magnetic sheet is rotatably accommodated in a jacket for handling and storage of the magnetic sheet. This type of magnetic cartridge is described in U.S. patent application Ser. No. 383,206 and U.S. Pat. No. 4,511,944 and is schematically represented by FIGS. 1 and 2 of the annexed drawings. In this case, the magnetic sheet 1 is rotatably accommodated in a magnetic sheet jacket 5 having an upper and a lower jacket part or half 3 and 4, said sheet or disc 1 being mounted on a center core or hub 2 which can be connected to not shown driving means.
The jacket 5 has a window 6, which faces a radial zone of the disc and through which a magnetic head 7 of the electronic still picture camera is inserted, and an opening 8, through which a motor drive shaft of the camera is inserted and connected to the center hub 2 of the disc 1. The jacket 5 is also provided with a rotatably counter display member 10 mounted outside the disc circumference in a corner area of the cartridge. The counter display member 10 has a keyhole-shaped aperture whose radial projection forms a pointer 13, pointing at a graduation of a display scale 14, provided on the upper side of jacket 5 around the counter display member 10.
The counter display member 10 is associated with a claw-clutch mechanism provided in the electronic still picture camera and able to enter the keyhole shaped aperture and to rotate the counter display member 10 intermittently step by step along a circular arc of predetermined length and angle, said display member 10 being linked to the magnetic head 7 so that its angular position corresponds to a determined position of the magnetic head which moves radially during an image sensing or recording cycle. The pointer 13 of the counter display member 10 indicates a numbered point on the display scale 14, by which the user may know the number of corresponding recorded tracks.
As the user may therefore know the number of recorded tracks, he may avoid overlapped recordings i.e. recordings of a plurality of different series of image signals on a single recording track, or skipping of non-recorded tracks.
However, when the known counter display member 10 is unintentionally or inadvertently rotated, the user can no longer know the accurate number of recorded tracks and the magnetic head 7 will no longer be correctly positioned with regard to its track, so that overlapped recordings or other undesired results will occur.
Furthermore, it may happen that the user removes the cartridge or jacket 5 from the camera body after having, for instance, taken 20 frames of images or pictures on a magnetic disc or sheet 1 having a capacity of 50 frames or pictures, and subsequently reinserts the jacket for recording images on the remaining unrecorded parts or tracks of the magnetic sheet 1.
In this case, the reinsertion of the jacket 5 into the camera body causes the claw-clutch mechanism on the side of the camera body to detect the position of the pointer 13, and to enter the keyhole-shaped aperture of the counter display member while moving the magnetic head 7 to a predetermined tracking position corresponding to the detected pointer position. In this way, the 21st picture frame of image is magnetically recorded on the 21st track. Even in this case, similarly to the above mentioned drawback, overlapped recordings or other undesired results may occur unless inadvertent or involuntary rotation of the counter display member 10 is prevented.
In the known magnetic sheet jacket 5, one tries to avoid this kind of involuntary rotation of the counter display member 10 with the help of a click and pawl arrangement in which a series of teeth 11 is formed on the periphery of the display member 10 and a click member 12 is elastically meshed in one of the spaces between said teeth. This locking arrangement does not however prevent with certainty involuntary rotation of the counter display member 10.